The present invention relates to orthopedic implants, and more particularly to implants of the femur.
One of the most frequently performed orthopedic surgical procedures involves implantation of devices designed to stabilize femoral fractures. These devices stabilize fractures of the femoral neck, intertrochanteric and subtrochanteric regions, and distal femoral condyles. Fractures which might once have left a person wheel-chair bound, can now be effectively treated with femoral implants.
Four classes of intertrochanteric fractures are currently treated with implants. A Type I fracture is a simple fracture across the intertrochanteric area without any bone displacement. Type II fractures are also across the intertrochanteric area, but the head and upper trochanteric segment are additionally displaced. A Type III fracture is unstable and more complex, usually having fracture lines in the lesser trochanteric area. The most severe fractures, Type IV, involve fragments in the area of the lesser trochanter and may extend into the subtrochanteric area. These fractures are the most difficult to reduce to a stable position.
In Type III and IV intertrochanteric fractures, large unstable bone fragments exist in the lesser trochanteric area. Fracture alignment in these severe breaks is difficult to maintain. Excessive collapse can occur resulting in a shortening of the femur (loss of leg length) leading to poor clinical results.
Implants are designed to provide an internal splint which holds the fracture in alignment while healing occurs. Some more recent implants have additional components for stabilizing fractures of the femoral shaft.
Current designs use an elongated lag screw with a distal threaded portion that is advanced through the intertrochanteric area and femoral neck finally gripping the femoral head. The lag screw of these designs slides inside a hollow barrel which allows pressure across the fracture as weight bearing occurs. The hollow barrel is part of a cortical side plate called a barrel plate. The plate portion of the barrel plate is attached to the cortical wall, and the barrel portion extends into the trochanteric area of the femur.
These early femoral lag screws and barrel plates allowed for a much more rapid patient recovery by providing internal support for hip fractures. The elongated lag screw was engaged in the barrel providing a telescoping means for final fracture reduction and compression at the fracture site.
Other types of femoral implants have comprised, in addition to the lag screw, an intramedullary rod or cortical side plate (see, for example, U.S. Pat. No. 4,776,330 to Chapman, et al). In the system described by the Chapman et al. patent, the intramedullary rod provided stabilization for subtrochanteric and femoral shaft fractures. The cortical side plate of Chapman et al. could be used with a lag screw and lower removable extension plate of varying lengths to provide stability for trochanteric fractures. The side plate was fastened to the femur with cortical screws, while the barrel held the lag screw.
The Chapman, et al. implant could be used where femoral neck or intertrochanteric fractures were combined with subtrochanteric or shaft fractures in a single injury. With this system, the side plate could be extended in length with a lower removable portion being slidably engaged with the upper side plate. The lower portion normally provided the surgeon with additional mounting holes for attaching the lower portion to the cortical surface of the shaft. The lower side plates were slidably engaged with the upper side plates by various methods including a "dovetail" construction shown herein as FIG. 1.
In previous designs, such as the "dovetail" the lower side plate was uniformly thinner in size than the upper side plate and therefore inherently possessed less tensile strength. This strength limitation is undesirable in implant devices that need to withstand heavy bending forces.
By choosing between various embodiments of the lower slide plate, the physician could then select the proper number of mounting holes appropriate for the type of fractures of the particular patient's femoral shaft. For example, more distal shaft fractures would require longer lower plate extensions. The interchangeability of the lower side plate gave the physician a greater range of implant embodiments from which to choose for any given femoral fracture.
In some unstable fractures, large segments of the medial wall are broken loose in the area of the lesser trochanter. Devices which are currently available do not provide screw hole positions that allow these loose fragments to be stabilized.
Accordingly, it would be an important improvement in the art to provide a femoral implant which provides a wide angle where the screws can be used to stabilize bone fragments in the lesser trochanter area. In addition, it would be advantageous to have a lower side plate which, when slidably engaged with the upper slide plate, locks into position and has a design which provides greater tensile strength to help prevent bending and breakage.